Most complex electronic devices use one or more printed circuit boards (PCBs) to provide both mechanical support and electrically conductive pathways to implement device functions. Variants and alternatives to PCBs include flexible circuits (also known as flex circuits or flex strips) and printed wiring boards.
Within PCBs, through holes (also spelled “thru-holes”) and vias are used to provide an electrical pathway between different layers of a multi-layered PCB. Within integrated circuits, electrical connections between layers are often referred to as “through-chip vias.” A via that extends to the exterior surface of a PCB or integrated circuit, and that connects to a metallic surface is referred to as a “contact” or “pad,” usubally providing electrical connectivity to the outside world.
Vias are constructed by mechanical drilling, and thus generally have a circular shape. Holes are made electrically conductive (and in some applications, thermally conductive) by electroplating a metallic coating, or by lining with a conductive tube or rivet. A drilled hole via that has been made conductive is referred to as a “barrel.” A via that is exposed only on one side of a PCB is called a “blind via,” while a via that only interconnects internal layers of a multi-layer PCB is called a “buried via”.
In present-day electronics, a via facilitates only a single electrical connection between layers within a PCB or a single contact with an external electrical component. In addition, electrical connections with metallic vias or pads are constructed using various processes (e.g., rework, reflow) involving soldering (melting of a metallic compound), exposing components to temperatures in excess of 200° C. with the potential to destroy or shorten the life of components.
The systems, apparatus, and methods herein draw from recent advances in the area of micro-fabrication. Micro-fabrication has generally benefited from systems and methods for precision positioning and micro robotics that are controlled by advanced computer-aided design software. The fabrication component draws from three areas in particular: 1) laser ablation to remove circuit substrate materials, 2) additive manufacturing, also commonly known as three-dimensional (3D) printing, and 3) micro-extrusion involving a continuous feed of materials with nano- and micro-scale feature sizes.
Laser ablation is a process of cutting or removing materials from a solid by irradiation with an intense laser beam. Although high-intensity laser radiation can convert a material into a plasma, lower intensity radiation that is absorbed by a material generally causes evaporation and/or sublimation of the solid material. Pulsed lasers (pulses durations ranging from milliseconds to femtoseconds) are frequently applied in laser beam machining; however, continuous wave lasers may also be employed.
By matching absorptive properties of materials to laser wavelength, material may be removed without significantly affecting or even heating surrounding materials, particularly when using short-pulsed lasers. This is particularly useful when laser machining holes, often referred to as “laser drilling.” Precision holes of almost any shape may be formed by steering a laser beam (e.g., using MEMS [micro-electro-mechanical systems] based or galvanic-controlled mirrors) or by moving a stage that holds the material being machined relative to a stationary beam.
Additive manufacturing or 3D printing refers to any of a variety of methods used to construct amorphic 3D objects by depositing successive layers of material under computer control. Sophisticated computer-aided design (CAD) programs are used to plan object construction (i.e., printing). Although there can be minor limitations on object form due to intricate structure or the effects of gravity, in general, there are few limitations on the overall shape of a constructed object.
One potential advantage of the systems, apparatus, and methods herein is the ability to precisely position different materials or insertions within a printed object. This may be performed by using separate printer “heads” and/or feeds for each of the different source materials. Most additive manufacturing techniques are amenable to the use and automated ability to select from multiple printer heads and/or material feeds.
More specifically, additive manufacturing using fused deposition involves the extrusion of small beads that quickly harden upon deposition. For example, thermoplastics (e.g., PLA, ABS) may be heated in the region of a nozzle and harden upon cooling following deposition. One or more nozzles may turn on or off the feeding of source materials to control both the geometry and heterogeneous composition of a 3D structure. Fused deposition methods may be used to construct objects made from polymers, plastics, eutectic metals, rubbers, silicones, ceramics, porcelains or clays.
Another additive manufacturing technique that is particularly amenable to the production of heterogeneous materials with programmed functionality is the binding of granular materials. Binding may result from either melting or sintering following the application of directed heat, laser light, or an electron beam. A wide range of metals, alloys, and thermoplastics may be used as base materials using these techniques.
A specific variant of the method of binding granular materials is 3D inkjet printing. Plasters or resins in a powder form (often impregnated with a thermoset polymer) are “printed” in layers using inkjet-like heads. Much like color printing, heterogeneous structures may be formed using multiple inkjet heads in the absence of excessive heating.
Photopolymerization involves the hardening of one or more liquid source materials by (generally ultraviolet) light. Printer systems using inkjets may also employ this methodology where each thin layer that is jetted is cured by exposure to ultraviolet light. A variant of this process involves curing liquids at selected locations using a laser (including more deeply penetrating multiphoton-based lasers) and washing away uncured liquid. These techniques are particularly useful for constructing small and ultra-small (i.e., with feature sizes <100 nm) objects.
Micro-extrusion and/or a continuous feed of materials may be used to produce segments of any length with complex cross-sections involving nano- and micro-scale features. Extrusion may be combined with continuous feed of separate materials (including materials that have been previously extruded) to produce multifaceted cross-sections with different functional regions. It is also necessary to carefully control both the physical and chemical properties of materials during extrusion and continuous feed processes.